Steam turbines

ABSTRACT

A steam turbine in which means for extracting water from wet steam has at least one drainage area in the turbine casing, with such area being located downstream of a row of rotatable blades adjacent the outlet for steam therefrom and intermediate the row of rotatable blades and an immediately adjacent downstream row of stationary blades, the drainage area comprising a plurality of circumferentially spaced elongated slots, the slots being disposed to lie transversely across the path of the wet steam in the region of the drainage area and being adapted for connection to a region which in operation of the turbine is at a lower pressure than the steam pressure in the region of the drainage area.

[72] Inventors Allen Smith; 1,165,922 12/1915 Wagner 415/168 Colin Trevor Moore, both of Newcastle 1,845,190 2/ 1 932 Reich 415/121 1 l N ggg g land FOREIGN PATENTS 5 gm Au 14 1969 210,881 11/1940 Switzerland 415/168 [45] Patented 361,819 6/1962 Switzerland..... 415/168 [73] Assignee C. A. Parsons & Company Limited 388,156 2/1933 Great Britain 415/168 Newcastle upon Tyne, England Primary ExaminerHenry F. Raduazo [32] Priority Aug. 21, 1968 Attorney-Holman & Stern [33] Great Britain 39987/68 ABSTRACT: A steam turbine in which means for extracting water from wet steam has at least one drainage area in the tur- [54] STEAM TURBINES bine casing, with such area being located downstream of a row 6 Claims,3Drawing Figs. of rotatable blades adjacent the outlet for steam therefrom 5 and intermediate matable blades and g 3 mediately adjacent downstream row of stationary blades, the [50] Field 415 21 drainage area comprising a plurality of circumferentially spaced elongated slots, the slots being disposed to lie transversely across the path of the wet steam in the region of the [56] Ref Ci drainage area and being adapted for connection to a region UNITED STATES PATENTS which in operation of the turbine is at a lower pressure than 745,045 1 1/1903 Emmet 415/121 the steam pressure m the region of the dramage area PATENIEB JR! 4 I972 SHEET 1 [IF 2 INVENTOR Y ALLEN SMITH ET AL BYAWJ M tha ATTORNEYS PATENTEBJAN 41972 31632225 SHEET 2 0F 2 INVENTOR ALLEN SMITH ET AL v BYfil-pam' I: I M! ATTORNEYS STEAM TURBINES This invention relates to steam turbines and is concerned with means for extracting water from wet steam in such turbines.

According to the present invention, an axial flow steam turbine comprises a turbine casing, a row of rotatable blades having tips and trailing and leading edges mounted within the casing, a row of stationary blades supported within the casing in spaced relationship to the rotatable blades downstream of the rotatable blades, and a drainage area between the rotatable blades and stationary blades for extracting water from wet steam flowing axially through the turbine casing, and drainage area including a circular wall carried by the turbine casing, said wall having upstream and downstream edges, with the upstream edge being immediately adjacent of the tips of the rotatable blades and the downstream edge upstream of but spaced from in unobstructed communication with the stationary blades, said wall being provided with a plurality of elongated longitudinal slots extending between the upstream and downstream edges along planes approximately containing the axis of rotation of the rotatable blades and being disposed transversely across the path of the wet steam in the region of the drainage area, the upstream edge of the wall being of a diameter of a circle defined by the tips of the rotating blades at their trailing edges, each of the slots having two opposed longitudinally extending edges disposed in a single surface of revolution common to all the longitudinally extending edges, whereby upon operation of the turbine, a substantially circumferentially flowing film of water moves from the rotatable blades and flows over the wall, and a region which, in operation, is at a pressure lower than the steam pressure in the drainage area and with which region the elongated slots communicate.

The invention also consists in a steam turbine with means for extracting water in accordance with the preceding paragraph in which the drainage area is connectable to a region at condenser pressure.

The invention also consists in a steam turbine with means for extracting water in accordance with the first of the preceding two paragraphs in which the drainage area is adapted for connecting to a feed heater.

The invention also consists in a steam turbine with means for extracting water in accordance with any of the preceding three paragraphs in which means are provided to keep the component of steam velocity normal to the turbine casing wall surrounding the rotatable blade row or to the drainage area in the turbine casing, or both, below a predetermined value such that rebound of water droplets from the wall of the casing is eliminated or minimized.

The invention also consists in a steam turbine with means for extracting water in accordance with the preceding paragraph in which the wall of the turbine surrounding the rotatable blade row or the slotted drainage area, or both, are shaped so as to reduce the angle of impact of water droplets.

The invention also consists in a steam turbine with means for extracting water from wet steam substantially as described hereinbelow with reference to the accompanying drawings.

Referring to the aforesaid drawings:

FIG. 1 is a cross section through part of a steam turbine showing means for removing water from wet steam in accordance with one embodiment of the present invention;

FIG. 2 is a view similar to FIG. 1 showing alternative means for removing water from the wet steam; and

FIG. 3 is a part section on line 3-3 of FIG. 1 and shows a typical form of drainage area for the turbine casing and suitable for use with the arrangements illustrated in FIG. 1 or FIG. 2.

ln carrying the invention into effect in the form illustrated by way of example and referring first to FIG. 1, an axial flow steam turbine comprises a rotor carrying rows of blades of which one row is shown at 1 and an outer casing 2 carrying rows of fixed stationary blades 3. A water drainage area denoted generally 4 is provided for the casing 2 downstream of the row of rotatable blades 1. This drainage area comprises a wall 4a having an upstream edge 4b and a downstream edge 40. The wall 4a is provided with a plurality of circumferentially spaced elongated longitudinal slots 5 which extend along planes containing the axis of rotation of the rotor from the edge 4b to the edge 40 and are disposed transversely across the path of the wet steam in the region of the area 4. Each slot 5 has opposed longitudinal edges 5a disposed in a single surface of revolution common to all slot edges.

The slots are connectable to or communicate with a region 5b at a lower pressure than that of the steam in the region of the drainage area. In one form, they are connected to an enclosure at condenser pressure.

Where the turbine has steam extracted at various stages for the purpose of feed heating, it is preferable to arrange the drainage area at a steam extraction stage.

It will be noted that wall 4a at the upstream edge 4b thereof is circular and is substantially equal in diameter to portion 2a of the turbine casing 2 surrounding the trailing edge In of the blades 1. In order words, the upstream edge of the wall is of a diameter closely approximating to, while being greater than the diameter of a circle defined by the tips of the blades 1 at their trailing edges.

In some circumstances, the extraction of water droplets from wet steam through the drainage area can be improved by arranging that the component of steam velocity normal to the casing wall surrounding the rotatable blade row is below a predetermined value so that rebound of the water droplets from the wall of the casing is eliminated or minimized.

FIG. 2 shows an arrangement for this purpose, with the end of the rotor blade having a sloping edge which is matched by a sloping wall in the casing. The shape of the turbine casing at the drainage area itself may also be arranged to reduce the angle of impact of water droplets thereon for the same reason.

FIG. 3 shows a section through part of the casing wall at the drainage area showing the slots 5.

If the wall portions between the slots of the slotted wall are sufficiently thick in relation to the slot width then their leading edges may be chamfered as indicated at 5c in FIG. 3 so as to prevent rebound of the water from the blunt edge back into the steam fiow.

The slotted extraction system shown offers a method of controlling the velocity or bled steam for any fixed total bleed quantity by varying either the number of slots or the slot gap which enables the water extraction rate to be optimized.

We claim:

1. An axial flow steam turbine comprising a turbine casing, a row of rotatable blades having tips and trailing and leading edges mounted within the casing, a row of stationary blades supported within the casing in spaced relationship to the rotatable blades downstream of the rotatable blades, and a drainage area between the rotatable blades and stationary blades for extracting water from wet steam flowing axially through the turbine, said drainage area including a circular wall carried by the turbine casing having upstream and downstream edges, with the upstream edge being immediately adjacent the leading edges of the tips of the rotatable blades and the downstream edge upstream of but spaced from in unobstructed communication with the stationary blades, said wall being provided with a plurality of elongated longitudinal slots extending between the upstream and downstream edges along planes approximately containing the axis of rotation of the rotatable blades and being disposed transversely across the path of the wet steam in the region of the drainage area, the upstream edge of the wall being of a diameter closely approximating to, while being greater than the diameter of a circle defined by the tips of the rotating blades at their trailing edges, each of the slots having two opposed longitudinally extending edges disposed in a single surface of a revolution common to all of the longitudinally extending edges, whereby upon operation of the turbine, a substantially circumferentially flowing film of water moves from the rotatable blades and flows over the wall, and a region which, in operation, is at a pressure lower than the steam pressure in the drainage are with which the slots communicate.

2. The steam turbine as claimed in claim 1 in which said region with which the drainage area communicates is at condenser pressure.

3. The steam turbine as claimed in claim 1 in which the region with which the drainage area communicates is a feed heater.

4. The steam turbine as claimed in claim 1 in which said wall is generally conical in configuration, and the interior of the turbine casing surrounding the rotatable blades and the stationary blades being generally conical in configuration, and

the interior surface of the turbine casing surrounding the rotatable blades having a cone angle substantially greater than that of the wall and the inner surface of the casing surrounding the stationary blades.

5. The steam turbine as claimed in claim 1 in which the surface of revolution common to all of the longitudinally extending edges of the slots is a cone.

6. The steam turbine as claimed in claim 1 in which the surface of revolution common to all of the longitudinally extending edges of the slots is a cylinder.

i t i 

1. An axial flow steam turbine comprising a turbine casing, a row of rotatable blades having tips and trailing and leading edges mounted within the casing, a row of stationary blades supported within the casing in spaced relationship to the rotatable blades downstream of the rotatable blades, and a drainage area between the rotatable blades and stationary blades for extracting water from wet steam flowing axially through the turbine, said drainage area including a circular wall carried by the turbine casing having upstream and downstream edges, with the upstream edge being immediately adjacent the leading edges of the tips of the rotatable blades and the downstream edge upstream of but spaced from in unobstructed communication with the stationary blades, said wall being provided with a plurality of elongated longitudinal slots extending between the upstream and downstream edges along planes approximately containing the axis of rotation of the rotatable blades and being disposed transversely across the path of the wet steam in the region of the drainage area, the upstream edge of the wall being of a diameter closely approximating to, while being greater than the diameter of a circle defined by the tips of the rotating blades at their trailing edges, each of the slots having two opposed longitudinally extending edges disposed in a single surface of a revolution common to all of the longitudinally extending edges, whereby upon operation of the turbine, a substantially circumferentially flowing film of water moves from the rotatable blades and flows over the wall, and a region which, in operation, is at a pressure lower than the steam pressure in the drainage are with which the slots communicate.
 2. The steam turbine as claimed in claim 1 in which said region with which the drainage area communicates is at condenser pressure.
 3. The steam turbine as claimed in claim 1 in which the region with which the drainage area communicates is a feed heater.
 4. The steam turbine as claimed in claim 1 in which said wall is generally conical in configuration, and the interior of the turbine casing surrounding the rotatable blades and the stationary blades being generally conical in configuration, and the interior surface of the turbine casing surrounding the rotatable blades having a cone angle substantially greater than that of the wall and the inner surface of the casing surrounding the stationary blades.
 5. The steam turbine as claimed in claim 1 in which the surface of revolution common to all of the longitudinally extending edges of the slots is a cone.
 6. The steam turbine as claimed in claim 1 in which the surface of revolution common to all of the longitudinally extending edges of the slots is a cylinder. 